One embodiment of the present invention relates to catadioptric imaging optical system, exposure apparatus, and a device manufacturing method, and more particularly, to a projection optical system optimal for use in an exposure apparatus employed for manufacturing a micro-device such as a semiconductor element and a liquid crystal display element in a photolithography process.
In a photolithography process for manufacturing a semiconductor element or the like, an exposure apparatus is used to project and expose a pattern image of a mask (or reticle) on a photosensitive substrate (wafer, glass plate, or the like that is coated with photoresist) with a projection optical system. In an exposure apparatus, the projection optical system is required to have a higher resolving power (resolution) since integration of semiconductor elements and the like has become higher. The wavelength λ of the illumination light (exposure light) must be shortened and the image side numerical aperture NA of the projection optical system must be enlarged to satisfy the requirements for the resolving power of the projection optical system. Accordingly, a liquid immersion technique is known to increase the image side numerical aperture by filling an optical path between the projection optical system and the photosensitive substrate with a medium such as liquid having a high refractive index.
Generally, in a projection optical system having a large image side numerical aperture, the employment of a catadioptric imaging optical system is desirable from the viewpoint in which the Petzval condition can be satisfied and flatness of an image can be obtained even in a dry system without being limited to the liquid immersion system. Further, the employment of an off-axis field imaging optical system in which an effective field of view (ultimately, an effective imaging region) does not include an optical axis is desirable from the viewpoint in which it can be applied to any fine pattern. In International Publication Pamphlet No. WO2005/069055, a thrice imaging type optical system including two reflection mirrors has been proposed as an off-axis field catadioptric imaging optical system optimal for use in an exposure apparatus.